The present invention relates to apparatus for separating spent abrasive blasting media from debris loosened by an abrasive blasting operation.
Abrasive blasting apparatus and methods have taken various forms. Generally, an abrasive medium such as sand or steel shot is propelled at high velocity at the surface to be treated. The combined features of the abrasiveness of the medium and the high velocity at which it is propelled causes the surface to abrade, generating debris such as dirt, paint, and rust from the treated surface, along with excessively fine abrasive media particles. The abrasive medium is reusable if the debris can be separated therefrom.
Various means have been employed in the art to allow the spent abrasive and debris to be reclaimed and to some extent, to separate them from one another.
For instance, British Pat. No. 1,542,495 to Worldwide Blast Cleaning, Ltd., discloses a device in which the spent abrasive and debris are carried up a reclaim channel by the kinetic energy of the abrasive medium. In this apparatus the reclaim channel opens into a hopper which acts also as a plenum, substantially decreasing the velocity of the air stream accompanying the abrasive medium and debris. The reduced velocity air stream no longer sustains the abrasive medium, but it does carry off the debris.
It is well known to separate debris from recycled abrasive media by the use of air washing methods. In these methods, the relative densities of the medium and contaminants are used to advantage, since the medium generally is more dense than the contaminants. The contaminated medium is caused to fall along a line in substantially continuous fashion so that a uniform "falling curtain" is obtained. An air stream is supplied through the falling curtain to entrain the contaminants and carry them away so that substantially uncontaminated abrasive medium can accumulate at the bottom of the curtain.
The uniformity of a falling curtain is important because voids or openings in the curtain allow the air to pass uninhibited and at increased velocity. The resulting increased velocity at the fringes of such a void or opening removes useable large abrasive particles. The reduced air stream velocity and volume in the remainder of the curtain results in incomplete washing.
There is a need in the art for an apparatus for separating debris from spent abrasive in an abrasive blasting apparatus in which the separation is very completely effected by the formation of a uniform falling curtain, and in which auxiliary air flows for air washing can be avoided.